Embossing bowl



' sheet'material. Inv producing surface pattern leffects on sheet Patented Aug. 27, 1946 EMBOSSING BOWL Y i Raymond E. Thomas, Newburgh, N. Y., assignor to4 E. Ldu Pont Vde Nemours & Company, Wilg n,mingtom Del., a corporation of lDelaware Application July 31, 1943Serial No. 496,947

4 Claims.

This invention relates to the embossing of Vsheet materialandmore particularly to increasing the vlongevity of paper coun-ter rollers, known asbowls, in the roller embossing operation of material by means yof embossing, two methods are commonly used; namely, platel embossing and roller eml'aossingv Y In the plate embossing method thes'heet material is' pressed between a metal plate bearing the'desired design in Vrelief and a softer fibrous base which has the counter of the design onthe metalpiate. 4

' In the roller 'embossing method engraved metal rolls are used 'in coniunction with softer counter n "rolls or bowls, whichareusually m'adeof paper.

The paper bowls are "made by Yplacing paper discs or washers at right an'glesto'the axis of a metal mandril and thenforcing 'the paperV discs into intimate contact yby means of pressure, after which .the discs are secured in position by use of rigid metal end supports connected to the man- -dril. The'paper vbowl carries a 'pattern counter to the pattern on thelmetal roll.

In producing an embossed pattern by the rollerA embossing `method ons'het material, it isv passed *between the'metalroller'andthe' paper bowl using 'suiiicient :pressure and -heat'to secure the desired pattern. l

The heat is applied 'customarily by heating the metal'roll althoughiitiissometime's advantageous Y j-to fpreheat the material vbefore it contacts the Arollers and vuse Ya cool metal roll, to secure the desired pattern. For ydeeper patterns more heat or-'lpressure-usually areappliedthan 'for shallower designs: For pyroxylin coated fabrics, Vpressures of -to '50 Vtonsfat `they area of contact of the r.metal-andpaperrolls, and *temperatures of 200 F. to 300 vF'. are used. 'Coatedfabri'cs utilizing :synthetic resins'of a more 'thermoplastic nature 80 tons and temperatures as lowas 60 F. The

K .metal roll is -driven by a series of gears, chains,

orother'mechanical means, while the paper bowl may be turned 4either by 'the friction against the .Jnetalfroll and the sheet material or by a series of gears, chains; vor other mechanical meansV acting in conjunction with the means used to drive the metal roll.

In ,the embossing-of sheet material, such as a fare sometimes embossed at pressures as high as.

coatedfabrid the pressure and heat of the opera- 4hereinafter as the Y proceeds.

tion of the engravedroll. The deterioration is manifested by a crumbling and fdusting-off of the outer surface of the paper bowl and, in time, by the spalling of larger pieces which render the bowl unfit for use. y Y Y Y This invention has for anl object a method for treating paper embossing bowls to render them more resistant topowdering or'fiaking of the paper surface upon continued operation. YAriother object is to lengthen the useful lifeof paper embossing bowls beyond their ynormally expected operating period. Other objects will appear In the normal operation of a roller, embossing rmachine the customary method for using a new paper bowl is to wet the bowl with water and to bring the metal embossing roller in contact with the bowl, 4first'under low pressure and then with gradually increasing pressure until full operating pressure is attained. This method o f cuttingin a design allows a clear, well defined counter impression of the' engraved roll to be reproduced on the bowl. The machine thenmay be used to emboss sheet material for a considerable period of time without giving any trouble with the bowl under ordinary operating conditions. Occasionally the engraved roller andthe bowl may get out of register and give embossed designs which are not clear cut and distinct. This is corrected by wetting the bowl with water, thereby swelling the paper bers and obliterating the previous design. The original process of cutting-in the design may then be repeated.

After embossing a considerable quantity of sheet material in a roller embossing machine, the bowl begins to show signs of deterioration caused by the pressure, heat and abrading action of the operation. This deterioration manifests itself in a hardening, crumblingor dusting-off of the surface of the bowl. At first the dust is a potential source of damage to the material merely because of the dirt contamination involved, but

soon the 4deterioration progresses to such an extent that a satisfactory grained material cannot be ysecured because of the poorly defined counter impression of the bowl. In certain cases where an embossing cylinder of a smaller size is available the bowl may be turned down on a lathe in the yconventional manner. In most cases the paper is removed to a depth o'f a quarter of an inch. The Ysame process is-thenfollowed as with a new ybowl in preparing and using it for embossing. In time the"turned down bowl will deteri- .Orate on the surface and must be discarded unless description of theV invention water soluble resin may be applied to the sur face of the manufactured bowl or may be incorporated into the paper before it is placed on the bowl mandril. A convenient method is to impregnate the formed paper sheet before it `is cut into sections; another method is to incorporate the resin directly'in the slurry from which the sheet of paper is formed.V

In the case in which a bowl is turned down for use with another cylinder after the bowl first shows signs of failure, the impregnating composition mentioned above also is of value as it tends to minimize the depth of deterioration. Normally deterioration, embrittlement and-hardening will take place to a greater depth than the l@ inch removed on the lathe. When the impregnating solution is used, this deterioration does not take place to any extent at depths of 1A; inch or more and in this manner affords a resilient -surfaceon a turned down bowl.

In the preferred embodiment of the invention a solution of polyvinyl alcohol, dissolved in water and Vplasticized with glycerine or similar water soluble polyhydric alcohol is applied to the surface of the bowl in sufcient quantity to impregnate the surface layers thoroughly. The bowl is thenV subjected to the cutting-in process previouslydescribed. The heat and pressure of the cutting-in process evaporates the water and leaves the paper fibers of the bowl impregnated with the polyvinyl alcohol-glycerine mixture.

In the drawing, Figure 1 represents a( diagrammatic section of an embossing bowl prepared according to the present invention. Figure 2 is a diagrammatic section of the bowl of Figure 1 in combination with a conventional embossing roll bearing a design. In both gures the same numerals refer to the same parts of which 4 is a mandril provided with a flange against which a large retaining washer I is placed. The paper discs which have been impregnated with polyvinyl alcohol or which subsequently may be coated with it are threaded onto the mandril. When sufficient of the paper discs have been mounted on the mandril another similar washer l is placed against them and forced together tightly by means of nutI 3. After the paper discs have been suiciently compressed and treated with a polyvinyl alcohol solution containing a plasticizer, the bowl is run under high pressure at elevated temperature against the embossing roll to cut in a counter design in the peripheries of the compressed paper discs. Subsequently a fabric 5 may be embossed by passing it between the bowl and the embossing roll as shown in Figure 2. The coated fabric is then wound up in a conventional manner on wind-up roll 6.

The following description of the preferred embodiment is given as an illustration. This description is not to be construed as limiting the invention to this preferred embodiment.

A bowl which had been used in the mbOSS- ing of material with a deep character, or grain, was beginning to show "dusting off of the surface. This would normally have resulted in the replacement or turning-down of the bowl. In this case, however, the bowl was given a liberal brush coating of the following solution while the embossing cylinder was operating in contact with the bowl under approximately 50 tons pressure and 270" F. temperature:

Bowl preservative composition nPart A: Per cent Polyvinyl alcohol 4.00 Water 40.50 Part B-Glycerine 26.50 Part C`Water 29.00

The above composition was prepared by making a slurry of the polyvinyl alcohol and cold water of part A. This slurry was then mixed while being heated in a steam jacketed kettle to give a lump-free clear dispersion. Part B was then added while the mixture was stirred, and the water of part'C was added hot with continued stirring to give the finished composition.

When applied to the bowl which was operating in the normal manner in conjunction with the embossing cylinder as described above, the heat of the cylinder served to evaporate the water and give a bowl whose outer surface was saturated with the polyvinyl alcohol, glycerine mixture. This mixture served to bind the paper bers together and prevent the crumbling and dustingoif which causes the bowl to become useless.

The bowl which was treated as described above was used in normal operation for more than two months before it was necessary to replace it. This added service represents a definite economic advantage.

The primary use of the invention is' to increase the useful life of paper bowls used in the roller embossing of sheet material. The invention will also find wide use where paper or other water absorbent materials are subjected to repeated or prolonged high pressures and high temperatures.

The treatment of roller embossing bowls with plasticized polyvinyl alcohol solutions inhibits deterioration of the surface of the bowl to such an extent that it may be used far beyond its normal period of usefulness. Another advantage is that when applied to new bowls and occasionally during the normal life of the bowl, deterioration will not only be retarded but will also not take place to as great a depth. 'Ihis latter behavior permits the bowl to be more readily turned down to a Isamaller size and still have a resilient, undeteriorated surface. Other advantages will be apparent to those Skilled in the art.

It is apparent that many widely different embodiments of this invention may be made without departing from the spirit and scope thereof, and therefore, it is not intended to be limited except as indicated in the appended claims.

I claim:

1. An embossing bowl capable of being cut in by a counter embossing roll to form a clear well defined impression and also highlyresistant to temperatures up to about 300 F. comprising a large number of centrally perforated paper discs impregnated at least on their periphery with a water soluble polyvinyl alcohol composition, a mandrel passing through the said perforations and end plates forholding the discs in compressed relation.

. 2. The bowl of claiml 1 in which the paper is impregnated with a composition consisting of polyvinyl alcohol, glycerine and Water.

I3. The bowl of claim 1 in which the paper is impregnated with a composition containing 4 parts of polyvinyl alcohol and 26.5 parts of glycerine. i

4. A method of treating paper embossing bowls 10 

